Magnetic nanoparticles (such as Fe3O4 nanoparticles) have unique properties of nanomaterials, such as small particle size, large surface area, higher coupling capacity, and the like. Meanwhile, they also have magnetic responsiveness and superparamagnetism, capable of gathering and positioning in a constant magnetic field and absorbing electromagnetic waves to generate heat in an alternating magnetic field. In addition, the magnetic nanoparticles can also be subjected to surface modification with a variety of active functional groups (such as —OH, —COOH, —NH3, etc.). Thus, the magnetic nanoparticles have broad application prospects in the biomedical fields for, for example, such as bio-separation, drug delivery, hyperthermia therapy for cancer, and the like, and have received extensive attention.
In biological and medical fields, a magnetic microsphere usually refers to a magnetic polymer microsphere, which is a magnetic material developed in recent years, typically manufactured by forming magnetic composite microspheres by combining magnetic inorganic particles (such as Fe3O4) with organic polymer materials. Prior magnetic microspheres can be provided with a variety of functional groups on their surfaces by means of surface modification or the like and therefore have been widely applied in the fields of biology, cytology, separation engineering, and the like. Particularly, the magnetic microspheres have outstanding advantages in biological separation and purification, immunoassays, biological testing, and similar areas, for being easy to use, fast, and efficient, among other features.
Magnetic microspheres for biological separation typically require the following properties: (1) superparamagnetism; (2) uniform particle size; (3) good dispersion in an aqueous phase; (4) low non-specific adsorption; (5) surface chemical groups available for modification. Magnetic microspheres also have significant advantages in proteins separation. For example, magnetic separation techniques can be applied in large-scale operations; the separation process may be performed directly in raw samples containing suspended solid particles or other biological particles; and, the separation process is simple and fast.
However, non-specific adsorption of proteins on the surface of magnetic microspheres is disastrous for their use in bio-separation. It will not only damage the specific separation effect by microspheres, but also increase background signal in a quarantine assay, decreasing the signal to noise ratio. A typical strategy to prevent non-specific adsorption of proteins on magnetic nanoparticles or magnetic microspheres is to perform surface chemical modification.
Patent Document CN102746529A discloses a method for preparing monodisperse magnetic microspheres by emulsion polymerization. However, the magnetic microspheres prepared by this method suffer from high non-specific adsorption of proteins, rendering a high signal-to-noise ratio in immunoassays. In addition, such method is too costly for industrial production.
Patent Document CN92105584.6 discloses a method for preparing immune magnetic microspheres by suspension polymerization. In this method, γ-Fe2O3 or Fe3O4 magnetic powders are surface-modified with long-chain fatty acids and then subjected to suspension polymerization in a styrene solution to generate the immune magnetic microspheres. Though the magnetic microspheres prepared by this method are low cost, they are high in non-specific protein adsorption yet poor in aqueous dispersibility.
Wang et al. used a porous γ-Fe2O3@ SiO2 magnetic silica as the matrix. An epoxy-modification was performed first, followed by forming a diol group by opening the ring of the epoxy group on the outer surface using a polymer acid with a particle size of 50 μm, reacting the remaining epoxy groups on the inner surface with octadecylamine, sodium bisulfite, and triethylamine hydrochloride, respectively, and eventually generating a novel magnetic restricted access material with octadecyl group, sulfonic acid group, and quaternary ammonium salt group in sequence on the inner surface and with diol group on the outer surface (Wang Yu. Novel preparation technology for biological samples based on restricted access functionalization of magnetic microspheres [D], Tianjin University, 2012). The diol group on the outer surface of the material can play a role in protein exclusion, while the magnetic restricted access material with sulfonic acid group and quaternary ammonium salt group on the inner surface has a much higher adsorption volume for small molecules than a material with octadecyl group on the inner surface. However, the preparation method of magnetic microspheres disclosed in this paper is relatively complicated, while their specific separation effects for biological proteins remains disputed.